A Study Of T Cell Vaccination On Inducing Xenogeneic Immunological Tolerance In An Islet Cell Transplantation Model

Previous studies have confirmed that T-cell vaccine can suppress immune rejection in the heart and liver allograft rejection and extend the graft survival time. There are few reports about TCV in the induction of xenogeneic transplant immune tolerance. Xenogeneic islet cell transplantation is potential to cure Type I diabetes mellitus (IDDM) with its advantages of sufficient source of donor, but the xenogeneic rejection limited its wide application. It is crucial to solve the problem that how to induce immune tolerance of xenogeneic pancreatic islet cell transplantation. T cell vaccination is a potential method of inducing transplantation immune tolerance. In this study, donor antigen specific TCV was used to immunize recipients before transplantation and the blood glucose and body weight changes were monitored after xenogeneic islet cell transplant.Objectives:To explore the effects of T cell vaccination on inducing xenogeneic islet transplant toleranceMethods:Type I diabetes mice model were made by injecting streptozotocin intravenously. Wistar rat pancreas.was harvested and islet cells were isolated from Wistar rat pancreas using the protocol of enzyme digestion and density gradient centrifugation. It is certain to maintain aseptic technique in the whole process. T cell vaccine was made by using attenuated spleen lymphocytes from Balb/c mice which were challenged with Wistar rat spleen lymphocytes(1:1) in vitro and were stimulated with Con A. Type I iabetes mice were randomly divided into three groups, Group A:Diabetic mice with no transplantation and no TCV, Group B(control group):Islet cell transplantation+PBS, Group C (experimental group):Islet cell transplantation+TCV. Balb/c mice as recipients were immunized with TCV on the time points of d-14, d-7 and d-1; PBS was used in control group. Islet cells were transplanted into immunized Balb/c mice at the density of 1500IEQ/one by the way of portal vein injection.Recipienf's blood glucose was monitored everyday and body weight was recorded weekly after transplantation.One-way mixed lymphocyte reaction (MLR) was performed with effector of immunized Balb/c mice peripheric lymphocytes and stimulator of Wistar rat peripheric lymphocytes on the fifth day of T cell vaccination.Results:It is successful IDDM models when blood glucose levels of Balb/c mice rose to 16.7mmol/1 and kept stable through the 5th day. Islet cells were stained with DTZ to comfirm the Islet cells, production reached (3570±356) IEQ/pancreas, the purity reached 70%-80%, AO-PI staining islet cells, live rate reached 80%-90%.The lever of blood glucose in mice before islet cell transplantation during the observation period:the diabetic mice group(21.5±1.46)mmol /1,thePBSgroup(20.6±1.57)mmol/l,theTCVgroup(22.3±1.37)mmol/l.Islet cell transplantation:The non-transplanted group showed a sustained high blood glucose levels, The blood glucose levels of the transplanted mice began to decline after 24h. The blood glucose value of the PBS group was (11.2±0.86) mmol/1 in the3th days after transplantation and reached the lowest value (9.2±1.36) mmol/1 in 4th days after transplantation. The value reached(19.4±1.53)mmol/l in the 8th days after plateau of 2 days.The blood glucose value of the TCV group was(11.8±1.84)mmol/l in the3th days after transplantation and reached the lowest value (6.4±1.67) mmol/1 in 6th days after transplantation.The value reached(19.5±1.22))mmol/l in the 24th days after plateau of 14 days.The changes in body weight of each group is similar to each other before islet cell transplantation. TCV group and PBS group body weight increased gradually after normal blood glucose levels, PBS began to decline in the d10 after transplantation. The TCV group continued to increased to d26 after transplantation. MLR results showed that comparison of the average OD value in different groups:There was no difference between the TCV group and PBS group before vaccination.The average OD value of group TCV was significantly lowered than the PBS group in the same time after vaccination(P<0.01). There was significantly difference before and after immunization.There was no difference statistically between different time point in the PBS group. Inhibition rate of the TCV group increased with the frequency of vaccination.Conclusion:T cell vaccination can significantly prolong the survival time of xenogeneic pancreatic islet grafts; T cell vaccination is a potential approach to to induce xenogeneic islet transplant tolerance.